Lockable trigger mechanism for use in an electrical device

ABSTRACT

A lockable trigger mechanism for an electrical device, comprising: a housing; a trigger for biased movement relative to the housing; an actuator movably mounted to the housing such that in response to operation of the trigger, the actuator is movable along a movement axis from an OFF position inwardly of the housing towards an ON position, and movable along the movement axis from the ON position in a direction outwardly of the housing towards the OFF position; an electrical switch unit mounted to the housing for activation in response to movement of the actuator along the movement axis between its ON and OFF positions to close and open an electrical circuit of the electrical device respectively; and a locking mechanism comprising a first locking member, a second locking member and a biasing member configured for biasing movement of the first locking member relative to the second locking member.

This application claims priority to Hong Kong Patent Application No.16111468.2 filed on Sep. 30, 2016, the content of which is incorporatedby reference in its entirety.

TECHNICAL FIELD

The present invention relates to lockable trigger mechanisms for use inelectrical devices such as a power tools, gardening tools and the like.

BACKGROUND OF THE INVENTION

It is sometimes required that a trigger-operated electrical device, suchas a power tool, be continuously operated for an extended period of timeat a desired speed setting. To alleviate fatigue in the user's fingeroperating the trigger, a locking mechanism may be provided to allowlocking of the power tool at the desired speed of operation. Certainconventional trigger mechanisms may include a latch member disposed onthe side of the trigger mechanism housing which must be manually movedwith some degree of force into a locking position by one of the user'shands to effect locking of the trigger mechanism in to the desired speedsetting. This is not only slow and tedious to lock the trigger mechanisminto the desired speed setting, but is also slow and tedious tothereafter dislodge the latch member from its locked position.Furthermore such conventional locking systems may also compromise usersafety as the user is required to use both hands to effect locking ofthe power tool. That is, one hand (usually the hand that is used tofirmly grip/support the body of the power tool) is required to manuallymove the latch member disposed on the trigger housing with some forceinto its locked position whilst the other hand is required to squeezethe trigger at the desired speed setting. Other conventional lockingsystems may require the latch member to be moved in multipleorientations, for instance, by manually moving the latch member inwardlyand then upwardly of the trigger housing. Again, these conventionallocking mechanisms require two hands to be operated and risk of injuryto the user is further exacerbated due to the awkward and unnaturalmovements required by one of the user's hand in manually moving thelatch member in to the locked position.

SUMMARY OF THE INVENTION

The present invention seeks to alleviate at least one of theabove-described problems.

The present invention may involve several broad forms. Embodiments ofthe present invention may include one or any combination of thedifferent broad forms herein described.

In a first broad form, the present invention provides a lockable triggermechanism for an electrical device, comprising: a housing; a triggerconfigured for biased movement relative to the housing; an actuatormovably mounted to the housing such that, responsive to operation of thetrigger, is movable along a movement axis from an OFF position in adirection relatively inwardly of an opening in the housing towards an ONposition, and movable along the movement axis from the ON position in adirection relatively outwardly of the opening in the housing towards theOFF position; an electrical switch unit mounted to the housingconfigured for activation in response to movement of the actuator alongthe movement axis between its ON and OFF positions to close and open anelectrical circuit of the electrical device respectively; and a lockingmechanism comprising a first locking member, a second locking member anda biasing member configured for biasing movement of the first lockingmember relative to the second locking member; wherein, responsive to theactuator being moved in a direction inwardly of the housing along themovement axis from its OFF position into its ON position, the firstlocking member is moved relative to the second locking member intoengagement with a first shape contour of said second locking member andsaid first locking member is held in engagement with the first shapecontour of said second locking member by the biasing member urging thefirst and second locking members together whereby the engagement of thefirst locking member with the first shape contour of the second lockingmember is configured to restrict movement of the actuator in a directionoutwardly of the housing along the movement axis from the ON position toits OFF position, and thereafter, responsive to the actuator being movedfurther in a direction inwardly of the housing along the movement axis,the first locking member is moved out of engagement with the first shapecontour of the second locking member and along a second shape contour ofthe second locking member whereby the movement of the first lockingmember along the second shape contour of the second locking member isconfigured to allow the actuator to be urged in a direction outwardly ofthe housing along the movement axis in to its OFF position.

Preferably, the biasing member may include an elastic member.

Preferably, the elastic member may include a coil spring.

Preferably, the biasing member of the locking mechanism may beconfigured for movement in substantially a same direction as the biasingmember of the actuator.

Preferably, the biasing member of the locking member may be configuredto function a dual-purpose as the biasing member of the actuator.

Preferably, the biasing member of the locking member may include areturn spring of the actuator.

Preferably, the first locking member may be disposed on an inner surfaceof the housing and the second locking member is disposed on theactuator.

Preferably, the first locking member may include a track and the secondlocking member may include a guide pin configured for slidable movementalong the track.

Preferably, the actuator may be configured to move along a linear axisinwardly and outwardly of the housing via the opening between the ON andOFF positions.

Preferably, the present invention may include a variable speed controlunit configured for controlling operation of the electrical device at aplurality of speeds, each of said plurality of speeds being controlledby reference to one of a plurality of corresponding positions of theactuator relative to the housing. Preferably, when the actuator is movedin a direction inwardly of the housing along the movement axis from itsOFF position into its ON position and the first locking member is movedrelative to the second locking member into engagement with the firstshape contour of said second locking member, the electrical device isconfigured to operate at a maximum speed of a plurality of possibleoperational speeds of the electrical device. Alternately, when theactuator is moved in a direction inwardly of the housing along themovement axis from its OFF position into its ON position and the firstlocking member is moved relative to the second locking member intoengagement with the first shape contour of said second locking member,the ON position may correspond to any one of a plurality of possibleoperational speeds of the electrical device.

Preferably, the electrical device may include at least one of a powertool and a gardening tool.

A lockable trigger mechanism for an electrical device, comprising: ahousing; a trigger configured for biased movement relative to thehousing; an actuator movably mounted to the housing so as to be movablealong a movement axis from an OFF position in a direction relativelyinwardly of the housing towards an ON position, and movable along themovement axis from the ON position in a direction relatively outwardlyof the opening in the housing towards the OFF position, said actuatorincluding a biasing member configured for biasing the actuator towardsthe OFF position; an electrical switch unit mounted to the housingconfigured for activation in response to movement of the actuationmember along the movement axis between its ON and OFF positions to closeand open an electrical circuit of the electrical device respectively;and a locking mechanism comprising a ballpoint pen type protract-retractmechanism configured for alternately retracting the actuator in to theON position in response to a first movement of the trigger relativelyinwardly of the housing, and thereafter, protracting the actuator in tothe OFF position in response to a further movement of the triggerrelatively inwardly of the housing.

Typically, the ballpoint pen type protract-retract mechanism maycomprise a plunger terminating in a set of teeth, a ratchet operablyconnected to the actuator, said ratchet having a set of main teeth, anda set of teeth disposed on an inner surface of the housing configuredfor alternately engaging and turning the main teeth of the ratchet topermit entry of the main teeth of the ratchet into slots disposed on theinner surface of the housing and for retaining the ratchet in theretracted position.

Typically, the ratchet may further include an inwardly positioned set ofauxiliary teeth for contact with the plunger teeth when the plungerengages the ratchet.

In a further broad form, the present invention provides an electricaldevice including a lockable trigger mechanism in accordance with any oneof the broad forms of the present invention described herein.

Preferably the electrical device may include at least one of a powertool and a gardening tool.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thefollowing detailed description of a preferred but non-limitingembodiments thereof, described in connection with the accompanyingdrawings, wherein:

FIG. 1 shows a first side view of a first embodiment of the presentinvention with the actuator slid outwardly of an opening in a triggermechanism housing along a movement axis in to an OFF position;

FIG. 2 shows a perspective view of the first embodiment of the presentinvention with the actuator slid outwardly of an opening in the triggermechanism housing along a movement axis in to an OFF position;

FIG. 3 shows a first side view of a first embodiment of the presentinvention with the actuator slid inwardly of the opening in the triggermechanism housing along a movement axis in to an ON position;

FIG. 4 shows a perspective view of the first embodiment of the presentinvention with the actuator slid inwardly of the opening in the triggermechanism housing along a movement axis in to an ON position;

FIG. 5 shows a perspective partial exploded view of the first embodimentof the present invention with the actuator slid outwardly of the openingof the trigger mechanism housing along a movement axis in to an OFFposition;

FIG. 6 shows a perspective view of the actuator (with track disposedthereon), a return spring and a guide pin of the first embodiment of thepresent invention;

FIG. 7A shows a transparent reverse side view of the first embodiment ofthe present invention with the actuator slid outwardly of the opening inthe trigger mechanism housing along a movement axis in to an OFFposition;

FIG. 7B shows a transparent reverse side view of the first embodiment ofthe present invention with the actuator slid inwardly of the opening inthe trigger mechanism housing along a movement axis in to an ON positionwhereby the guide pin is urged into engagement with a first shapecontour of the track and is held in engagement to restrict movement ofthe actuator outwardly of the opening in the trigger mechanism housingalong the movement axis;

FIG. 7C shows a second transparent side view of the first embodiment ofthe present invention shown in FIG. 7B after the actuator has beenfurther slid inwardly of the housing along the movement axis so that theguide pin is moved out of engagement with the first shape contour of thetrack and along a second shape contour of the track to allow theactuator to be urged in a direction outwardly of the opening in thetrigger mechanism housing along the movement axis in to its OFFposition;

FIG. 8 shows magnified views of the guide pin seated within the housingand the track moulded into the actuator; and

FIG. 9 shows various aspects of an exemplary known ballpoint pen typeprotract-retract mechanism which may be configured for use inautomatically locking the actuator of the power tool in ON and OFFpositions responsive to movement of a trigger.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be describedherein with reference to FIGS. 1 to 9. The embodiments comprise avariable-speed trigger mechanism of an electric power tool having anovel locking mechanism for automatically locking the trigger mechanismat a desired speed setting so that the power tool may continue operatingat that speed setting without requiring the user's finger to continueholding the trigger in the speed setting position. The power tool mayinclude for instance an electric drill, grinder, sander, saw, rotarydriving tool and the like. It would be appreciated and understood thatwhilst this embodiment is described for use in locking a variable-speedtrigger mechanism of an electric power tool, this is merely for ease ofillustrating functionality and alternate embodiments of the presentinvention may of course be used for locking both single-speed as well asvariable-speed trigger mechanisms for use in any other type ofelectrical devices such as gardening tool.

Referring to FIGS. 1 and 2, the variable-speed trigger mechanismincludes a moulded plastic housing (900, 1000) that is mounted to a bodyof the electric power tool near to a handle of the electric power tool.The housing (900, 1000) includes a first housing member (900) and asecond housing member (1000) that may be snap-fitted or screwed togetherto substantially enclose the trigger mechanism and locking mechanismtherebetween. The variable-speed trigger mechanism includes afinger-operable trigger having an actuator (1200) configured forslidable linear movement relative to the housing (900, 1000) along amovement axis (X,X′) relatively inwardly of an opening in the housing(900, 1000) from an OFF position towards an ON position, and, relativelyoutwardly of the opening in the housing (900, 1000) from the ON positiontoward the OFF position. A sealing ring (700) is located at the openingof the housing (900, 1000) to provide a seal between the opening and theactuator (1200) which may alleviate ingress of dust and other particlesinto the housing (900, 1000) via the opening. A return spring (600) ismounted inside the housing (900, 1000) which bears upon an inner surfaceof the housing (900, 1000) to urge the actuator (1200) towards the OFFposition by default.

An electrical cord (not shown) is coupled to the housing (900, 1000)adjacent the cable cover (1100) and is also electrically coupled to anelectric motor (not shown) of the electric power tool (not shown) so asto be able to provide electrical power for driving the electric motor.While the embodiment described herein includes an electrical cord, otherembodiments of the present invention may be cordless and configured tobe driven by a lithium ion battery, a ni-cad battery, or the like.

As depicted most clearly in the transparent side-views of FIGS. 7A-7C,two pairs of electrical contacts (400-400′, 400-400′) are located insideof the housing (900, 1000) which define two electrical switches that areoperable in response to movement of the actuator (1200) between the ONand OFF positions for closing and opening individual electricalcircuits. The electric motor is driven by the power supply arranged inseries in a first electrical circuit when the first electrical switch isarranged in a closed state responsive to movement of the actuator (1200)inwardly of the housing (900, 1000). An auxiliary electrical elementsuch as a power-on indicator LED (500) is also driven by the powersupply arranged in series in a second electrical circuit when the secondelectrical switch is arranged in a closed state responsive to movementof the actuator (1200). Two of the electrical contacts (400, 400) aredisposed on the ends of the fixed electrical terminals (300A, 300C) thatare rigidly secured within the housing (900, 1000) whilst two of theelectrical contacts (400′, 400′) are disposed on the ends of a contactlever (1400) that is pivotably mounted to a common fixed electricalterminal (300B) which acts as a fulcrum for the contact lever (1400)mounted thereon. The contact lever (1400) is configured to pivotablymove in response to slidable movement of the actuator (1200) along themovement axis so that each contact pair (400-400′, 400-400′) are eitherin contact with each other in the ON state or out of contact with eachother in the OFF state. All of the electrical contacts (400-400′,400-400′) are formed from a copper alloy material with or withoutplating which may ensure good electrical contact after repeatedoperation of the electrical switches and alleviates sparking.

The variable-speed trigger mechanism includes a variable-speed controlmechanism for controlling the amount of power delivered to the electricmotor from the power supply and hence the speed of the motor, inresponse to movement of the trigger by the user's finger. In thisembodiment, the power tool may by way of example have 4 speed settingswhich correspond to different relative positions of the actuator as itis slidably moved inwardly of the housing (900, 1000) along the movementaxis (X,X′). As the trigger is squeezed and the actuator (1200) isgradually moved inwardly of the housing (900, 1000) along the movementaxis (X,X′), the speed of the power tool may incrementally increase fromspeed setting 1 (OFF) through to speed setting 4 (ranging for instancefrom 0 rpm through to 2,000 rpm). Each of the speed settings from 1through to 4 may be incrementally increased as the user squeezes thetrigger and the actuator (1200) moves increasingly relatively inwardlyof the housing (900, 1000) to certain threshold distances correspondingto each of the speed settings.

In this embodiment, the variable-speed control mechanism may include apotentiometer, a timing signal generator and a solid state device thatare operably-connected together so as to control the amount of powerdelivered to the motor from the power supply and hence the speed of themotor in operation, in response to the extent to which the trigger issqueezed by the user's finger. A PCB (100) is mounted within the housingadjacent the actuator (1200) and includes the timing signal generatorand solid state device circuitry thereon. The potentiometer includes aconductive wiper (200) which is mounted to the actuator (1200) so as tomove linearly along the movement axis (X,X′) relative to conductive padsof the potentiometer disposed on a PCB (100). In use, the conductivewiper (200) is configured to have current running therethrough such thatthe potentiometer will output a variable voltage signal in response tothe position of the wiper (200) relative to the conductive pads. Thetiming signal generator (e.g. a “555” circuit) is communicably coupledwith the output of the potentiometer and is configured to sense thevariable voltage signal of the potentiometer. The movement of theconductive wiper (200) relative to the conductive pads gradually reducesthe resistance of the potentiometer from a relative high resistancetowards a relatively low resistance, and the variable voltage signalsent to the timing signal generator will vary accordingly. The output ofthe timing signal generator is coupled to an input gate of a solid statedevice, such as a MOSFET, whereby in response to the received timingsignal, the MOSFET is configured to be switched on and off at timingintervals corresponding to the timing signal generator output toappropriately control the amount of power that is delivered from thepower supply to the electric motor corresponding to the conductive wiper(200) position (and hence speed setting).

The locking mechanism of this embodiment is integrally formed inside ofthe trigger mechanism housing (900, 1000) and allows the actuator (1200)to be automatically locked after the actuator (1200) has been slidablymoved relatively inwardly of the housing (900, 1000) along the movementaxis (X,X′) into the desired speed setting position. This obviates theneed for the user to manually lock the actuator (1200) into position anddoes not require the user to continue to manually holding the trigger inposition to maintain continued operation of the power tool at thedesired speed setting. In use, as the actuator (1200) is initially movedrelatively inwardly of the opening in the housing (900, 1000) from itsdefault OFF position along the movement axis to a desired ON speedsetting, the locking mechanism will function to releasably lock theactuator (1200) into its speed setting position such that the actuator(1200) is restricted from being moved in a direction relativelyoutwardly of the opening in the housing (900, 1000) along the movementaxis (X,X′) . The power tool will continue to operate at the speedsetting to which it is automatically locked without requiring the user'sfinger to continue manually operating the trigger. Thereafter, byfurther squeezing the trigger and causing the actuator (1200) to movefurther in a direction relatively inwardly of the opening in the housing(900, 1000) along the movement axis, the actuator (1200) may be easilyand conveniently unlocked from its speed setting and allowed to slideagain in a direction relatively outwardly of the housing (900, 1000)along the movement axis (X,X′) towards its default OFF position.

In this embodiment, the locking mechanism comprises a first lockingmember in the form of a guide pin (1300), a second locking member in theform of a track (1500), and a biasing member (600) in the form of a coilspring (600) configured for urging movement of the guide pin againstshape contours of the track (1500) as it is moved along the track(1500). Also in this embodiment, as shown in FIG. 8, the guide pin(1300) is mounted within a seating portion (1600) disposed in an innersurface of the first housing member (900) whilst the track (1500) ismoulded in to a surface of the actuator (1200) so as to be slidablymovable with the actuator (1200) as the actuator (1200) slidably movesinwardly and outwardly of the housing (900, 1000) along the movementaxis (X,X′). The track (1500) is also configured for receiving the guidepin (1300) so that the guide pin (1200) may slide along the track (1500)during movement of the actuator (1200). The guide pin (1300) is springloaded by a spring member (1300A) and is also able to swivel aboutwithin the seating portion (1600) of the first housing member (900) inwhich it is seated. In this embodiment, the biasing member (600) of thelocking mechanism is provided by the return spring (600) of the actuator(1200) which serves a dual-functional purpose. It is of course possiblefor the locking mechanism to include its own independent biasing memberin alternate embodiments whereby the biasing member of the lockingmechanism and the return spring of the actuator (1200) would beconfigured to expand and contract substantially in a same direction.However the shared use of the actuator (1200) return spring (600) alsoas the biasing member of the locking mechanism may assist in providing amore compact and simplified trigger and locking mechanism as well asreduced complexity and costs of manufacturing.

In response to the actuator (1200) being moved in a direction relativelyinwardly of the opening in the housing (900, 1000) along the movementaxis (X,X′) from its OFF position (as shown in FIG. 7A) into a desiredON speed setting (as shown in FIG. 7B), the guide pin (1300) mounted onthe housing (900, 1000) is configured to slide within the track (1500)and into engagement with a first shape contour (1500A) of the track(1500). The guide pin (1300) is configured to be held in engagement withthe first shape contour (1500A) of the track (1500) as shown in FIG. 8by the biasing member (600) urging the guide pin (1300) and track (1500)together whereby the engagement of the guide pin (1300) with the firstshape contour (1500A) of the track (1500) is configured to restrictmovement of the actuator (1200) in a direction relatively outwardly ofthe opening in the housing (9, 10) along the movement axis (X,X′) fromthe ON speed setting towards the OFF position. As shown in the magnifiedview of the track in FIG. 8, the guide pin (1300) would be urged in toengagement and held at region (1500A′) on the first shape contour(1500A) of the track by virtue of the biasing member (600) beingnaturally configured to urge the guide pin (1300) and track (1500)together. Thereafter, responsive to the actuator (1200) being movedfurther in a direction relatively inwardly of the opening in the housing(900, 1000) along the movement axis (X,X′), the guide pin (1300) isconfigured to slide within the track (1500) out of engagement with thefirst shape contour (1500A) of the track (1500) and along a second shapecontour (1500B) of the track (1500) as shown in FIG. 8 whereby themovement of the guide pin (1300) along the second shape contour (1500B)of the track (1500) is configured to allow the actuator (1200) to beurged in a direction outwardly of the housing (900, 1000) along themovement axis (X,X′) in to its OFF position (as shown in FIG. 7C).Advantageously, it can be seen that the locking mechanism provides anautomatic mechanism for locating the track (1500) and guide pin (1300)relative to each other to restrict movement of the actuator (1200) whenin the desired ON speed setting, and, the biasing member (600) assistsin automatically holding the guide pin (1300) against the first shapecontour (1500A) of the track (1500) thereby restricting movement of theactuator (1200) in a direction relatively outwardly of the opening inthe housing (900, 1000) without requiring any manual actuation by theuser to lock the power tool in to the speed setting. The power tool willalso continue to operate at the desired speed setting to which it isautomatically locked by the locking mechanism without requiring theuser's finger to continue operating trigger. The automatic lockingmechanism of this embodiment may also allow the power tool to be lockedone-handedly if required by simply squeezing the trigger to lock andsqueezing the trigger to unlock the power tool from a given speedsetting.

For illustrative purposes only, the example track (1500) configurationshown in FIG. 8 only shows a first shape contour (1500A) and a secondshape contour (1500B) for locking the guide pin (1300) into one ON speedsetting. In this embodiment, the position of the first shape contour(1500A) along the track (1500) is such that when the tip of the guidepin (1300) is held at region (1500A′) of the first shape contour (1500)to restrict movement of the actuator (1200) in a direction relativelyoutwardly of the opening in the housing (9, 10), the actuator (1200) ispositioned relative to the housing (900, 1000) whereby the electricpower tool is operating at a maximum speed setting. The trigger willtypically be fully squeezed inwardly of the housing (900, 1000) when theelectrical power tool is operating in its maximum speed setting. Itwould be understood by a person skilled in the art that in alternateembodiments, the track (1500) may be configured to include additionalshape contours to which the guide pin (1300) may engage with as itslides along the track (1500) in order to allow locking of the powertool at more than one speed setting—for instance, being lockable in themaximum speed setting, a minimum speed setting and an intermediate speedsetting. The plurality of shape contours may for instance take the formof a series of “stepped” shape contour regions positioned along thetrack (1500) against which the tip of the guide pin (1300) may beincrementally engaged with and held in engagement with to lock the powertool into each of the corresponding speed settings, as the actuator ismoved gradually inwardly of the housing (900, 1000).

It would be appreciated that in alternate embodiments, the arrangementof the guide pin (1300) and the track (1500) may be reversed such thatthe guide pin (1300) may instead be mounted on the actuator (1200)whilst the track (1500) may be disposed on the first housing member(900).

In a further embodiment of the present invention, the trigger mechanismmay comprise a locking mechanism having a protract-retract typemechanism similar to that used in a ballpoint pen forpush-to-retract/push-to-protract operation of the ink cartridge relativeto the pen barrel. The protract-to-retract type mechanism may beconfigured to alternately retract and lock the actuator in to the ONposition in response to a first movement of the trigger relativelyinwardly of the housing, and thereafter, protract and lock the actuatorin to the OFF position in response to a further movement of the triggerrelatively inwardly of the housing.

One example of a ballpoint pen type protract-retract mechanism which maysuitably configured for use in the locking mechanism of this embodimentis as described in U.S. Pat. No. 3,288,155 the content of which isherein incorporated by reference and selectively reproduced as followsfor the purpose of illustrating principle of operation. The pen shown inFIG. 9 comprises a cap (10), and a barrel (12), a cartridge (14), aretract spring (16), and a protract-retract type mechanism (18) foroperating the cartridge. The pen cap and barrel (12) may be threaded asat (20) and (22) respectively for securing the parts in position. A band(24) is sometimes used to secure better alignment between the cap andbarrel. The cap is preferably provided with a clip (26) which in the penillustrated is secured to the cap by a hollow rivet (28). Theprotract-retract mechanism (18) comprises in part, a plunger (30)terminating in an exposed push button (32) at one end, projectingthrough the opening (34) of the cap, and in a hub (36), made hollow asat (38), to receive the stem (39) of ratchet (40). The plunger (30) ispreferably formed with eight laterally extending guides (42), which areadapted to slide in slots (44) and (44 a) formed on the inner wall (46)of cap (10). The slots are positioned between rails (48) and (48 a)terminating in tapered teeth (50) and (50 a) respectively. The guides(42) of plunger (30) are always positioned in the slots (44) and (44 a)providing a longitudinal non-rotative movement of the plunger in cap. Inthe form illustrated, slots (48) are less deep than slots (48 a)although the slots may be of equal depth. The ratchet (40) is providedwith a hub (52) from which laterally extends four guides (54) eachprovided with a main tapered tooth (56) on the upper face thereof toengage the tapered teeth (50) and (50 a) of the rails (48) and (48 a) onthe inner surface of the cap (10). The lower edge of the plunger (30)terminates in eight teeth (58), which also engage the tapered teeth (56)on the four guides (54) of ratchet (40). By providing the upper edge ofthe hub (52) with an auxiliary set of eight circularly arranged taperedteeth (60), for engaging the eight teeth (58) formed on the bottom edgeof the hub (36) of plunger (30). Thus when ratchet (40) is inserted intothe bore (38) of plunger (30), the tapered teeth (58) of the plunger(30) and the tapered teeth (60) of the ratchet (40) are configured toengage each other and align the parts as is shown in FIG. 9 preventingthe sharp edges of tapered teeth (56) from cutting into the plunger andjamming the mechanism, preventing rotation of the ratchet. The design ofthe teeth of the plunger (30), ratchet (40) and cap (10), causes theratchet (40) to rotate slightly when released from the cap (10), andagain when the ratchet teeth engage the cap (10). The ratchet teethalternately move from the protracted position on teeth (50 a) into theretracted position when the ratchet teeth engage cap teeth (50) andslide into slot (44 a). From either position, the plunger (30) whenagain pressed, will free the ratchet (40) from the cap (10), allowingthe ratchet (40) to rotate slightly until the teeth lock, and then whendeposited once more on the cap (10) to rotate slightly again untilcaught in the protract position or the retract position, depending onthe position of the ratchet guides with respect to the cap slots. Thusthe ratchet (40) rotates slightly when depressed by the plunger (30),and again on the cap teeth when the plunger (30) is withdrawn, causing acircular movement that permits the cartridge to be alternatelyprotracted and retracted. The spring (16) operating on ears (66) of thecartridge (14), forces the cartridge (14) continuously against theratchet in bore (62), the bevelled seat (64) being provided in thebottom of the ratchet for facility in inserting the end of thecartridge. The stem (39) of the ratchet helps to maintain alignmentthereof throughout the protract-retract operation. The bevel of seat(64) is made possible by the extra hub diameter created by teeth (60).It will be seen that there is now provided a full uniform 360° contactbetween ratchet and the plunger teeth, except when the teeth engage ontheir tapered sides to initiate rotation. When the circular movementceases, the 360° contact is resumed. The added contact between theauxiliary ratchet teeth and the plunger teeth also frees the plungerfrom the ratchet to permit movement of the ratchet on the cap teeth,without jamming with the plunger teeth.

It would be appreciated that the protract-retract type mechanism asdescribed above may be suitably modified for use in the context of alockable trigger mechanism by configuring the housing of the triggermechanism with teeth and slots in an inner surface of the housing so asto take the place of the pen cap (10). The actuator of the triggermechanism is operably coupled to the ratchet inside of the housing, forinstance by seating one end of the actuator upon the ratchet so as totake the place of the pen cartridge (14). Furthermore, the exposed pushbutton (32) of the plunger (30) would be substituted with a springloaded-trigger that is operable by the user's finger to depress theplunger (30) relative to the ratchet.

Although the exemplary ballpoint pen protract-retract type mechanismdescribed herein has referred to the mechanism of U.S. Pat. No.3,288,155 for ease of understanding the principle of operation, it wouldbe understood by persons skilled in the art that any otherprotract-retract type mechanism may also be utilised in embodiments ofthe present invention to effect locking of the trigger mechanismactuator in the ON and OFF positions.

In view of the above, it will be apparent that embodiments of thepresent invention herein described may assist in providing at least oneof the following advantages:

-   -   (a) a faster and easier to use lockable trigger mechanism may be        provided by virtue of its one-hand operation and automatic        locking/unlocking operability;    -   (b) a safer to use lockable trigger mechanism may be provided by        virtue of its one-hand operation as this obviates the need for        the user's gripping/support hand to manually operate a latch        member as in the case of conventional mechanisms. Also, the user        may easily and quickly effect locking and unlocking of the        trigger mechanism at a desired speed setting with one hand        simply by squeezing the trigger in one linear motion thus        obviating the need for awkward and unnatural movement of an        external latch member in a multiple directions by the user's        gripping/support hand;    -   (c) a biasing member (e.g. a return spring) of the actuator may        be conveniently utilised to serve a dual-function as the biasing        member of the locking mechanism. Consequently, this results in a        more compact and simplified integrated trigger and locking        mechanism that may be neatly accommodated within a single        housing. This also reduces the number of component parts in the        integrated trigger and locking mechanism and alleviates overall        manufacturing costs.

Those skilled in the art will appreciate that the invention describedherein is susceptible to variations and modifications other than thosespecifically described without departing from the scope of theinvention. All such variations and modification which become apparent topersons skilled in the art, should be considered to fall within thespirit and scope of the invention as broadly hereinbefore described. Itis to be understood that the invention includes all such variations andmodifications. The invention also includes all of the steps andfeatures, referred or indicated in the specification, individually orcollectively, and any and all combinations of any two or more of saidsteps or features.

The reference to any prior art in this specification is not, and shouldnot be taken as, an acknowledgment or any form of suggestion that thatprior art forms part of the common general knowledge.

What is claimed is:
 1. A lockable trigger mechanism for an electricaldevice, comprising: a housing; a trigger configured for biased movementrelative to the housing; an actuator movably mounted to the housing suchthat, responsive to operation of the trigger, is movable along amovement axis from an OFF position in a direction inwardly of an openingin the housing towards an ON position, and movable along the movementaxis from the ON position in a direction outwardly of the opening in thehousing towards the OFF position; an electrical switch unit mounted tothe housing configured for activation in response to movement of theactuator along the movement axis between its ON and OFF positions toclose and open an electrical circuit of the electrical devicerespectively; and a locking mechanism comprising a first locking member,a second locking member and a biasing member configured for biasingmovement of the first locking member relative to the second lockingmember; wherein, responsive to the actuator being moved in a directioninwardly of the housing along the movement axis from its OFF positioninto its ON position, the first locking member is moved relative to thesecond locking member into engagement with a first shape contour of saidsecond locking member and said first locking member is held inengagement with the first shape contour of said second locking member bythe biasing member urging the first and second locking members togetherwhereby the engagement of the first locking member with the first shapecontour of the second locking member is configured to restrict movementof the actuator in a direction outwardly of the housing along themovement axis from the ON position to its OFF position, and thereafter,responsive to the actuator being moved further in a direction inwardlyof the housing along the movement axis, the first locking member ismoved out of engagement with the first shape contour of the secondlocking member and along a second shape contour of the second lockingmember whereby the movement of the first locking member along the secondshape contour of the second locking member is configured to allow theactuator to be urged in a direction outwardly of the housing along themovement axis in to its OFF position; and wherein, the first lockingmember includes a track disposed in a surface of the actuator, saidtrack being formed so as to project inwardly of the actuator surface ina direction substantially perpendicularly to the direction of themovement axis of the actuator, the second locking member including aspring-loaded guide pin mounted on an inner surface of the housing, saidguide pin being configured to extend inwardly of the housing from theinner surface of the housing in a direction substantiallyperpendicularly to the movement axis of the actuator and inwardly of thetrack, whereby responsive to the movement of the actuator inwardly andoutwardly of the housing the guide pin is configured to slidablytraverse the track.
 2. A lockable trigger mechanism as claimed in claim1 wherein the biasing member includes an elastic member.
 3. A lockabletrigger mechanism as claimed in claim 1 wherein the elastic memberincludes a coil spring.
 4. A lockable trigger mechanism as claimed inclaim 1 wherein the biasing member of the locking mechanism isconfigured for movement in substantially a same direction as the biasingmember of the actuator.
 5. A lockable trigger mechanism as claimed inclaim 1 wherein the biasing member of the locking member is configuredto function a dual-purpose as the biasing member of the actuator.
 6. Alockable trigger mechanism as claimed in claim 5 wherein the biasingmember of the locking member includes a return spring of the actuator.7. A lockable trigger mechanism as claimed in claim 1 wherein theactuator is configured to move along a linear axis inwardly andoutwardly of the housing via the opening between its ON and OFFpositions.
 8. A lockable trigger mechanism as claimed in claim 1wherein, when the actuator is moved in a direction inwardly of thehousing along the movement axis from its OFF position into its ONposition and the first locking member is moved relative to the secondlocking member into engagement with the first shape contour of saidsecond locking member, the electrical device is configured to operate ata maximum speed of a plurality of possible operational speeds of theelectrical device.
 9. A lockable trigger mechanism as claimed in claim 1wherein, when the actuator is moved in a direction inwardly of thehousing along the movement axis from its OFF position into its ONposition and the first locking member is moved relative to the secondlocking member into engagement with the first shape contour of saidsecond locking member, the ON position may correspond to any one of aplurality of possible operational speeds of the electrical device. 10.An electrical device including a lockable trigger mechanism inaccordance with claim 1.